Rice is one of the leading food crops of the world, second only to wheat in terms of annual production for food use. It is a staple food for about 60% of the world's population. Rice is a semi-aquatic, annual grass that can be grown under a broad range of climatic conditions. The principle parts of a rough rice grain are the hull, pericarp, seed coat, nucellus, embryo, aleurone layer, and endosperm. The hull is the outer covering of the caryopsis (brown rice). The hull comprises about 18-20% by weight of the rough rice grain and serves a protective function against insect infestation and environmental fluctuations. Removal of the hull from the rough grain rice by shelling exposes the caryopsis. The caryopsis comprises four distinct layers. These include the pericarp, seed coat, nucellus, and aleurone. Along with much of the embryo (i.e., germ), these layers comprise the bran portion of the rice grain. The bran portion accounts for about 5-8% of the brown rice weight and is the most nutritious part of the caryopsis.
Rice is consumed in two forms, brown rice and white rice. In both forms, the hull is removed from the rice grain through shelling to yield brown rice. White rice, however, is produced by removing the bran portion of brown rice through a process called “milling.” Brown rice is extremely high in nutritional value. Consumption of brown rice may lead to a more complete diet and may help prevent diseases such as high cholesterol, heart disease, and diabetes. Brown rice also has a desirable flavor. There are, however, some disadvantages with brown rice. For example, brown rice has a chewy texture, is more difficult to digest than white rice, and it takes longer to cook. Furthermore, brown rice has a poor shelf life; because brown rice contains the germ of the rice grain along with essential oils, if brown rice remains at room temperature for an extended period of time, the germ and essential oils may oxidize, leading to rancid odor and taste.
White rice has several advantages over brown rice. White rice is preferred by most consumers because of its appearance, its texture, and its shorter cook time compared to brown rice. White rice also has a longer shelf-life because the germ and essential oils are removed during the milling process. White rice, however, does have some drawbacks. First, the taste of white rice is often blander than brown rice. More significantly, white rice is much less nutritious than brown rice, because a majority of the nutritional value of rice is found in the bran. For example, white rice contains only about a fifth of the fiber found in brown rice, it has a much lower concentration of B vitamins and important minerals, and has substantially lower amounts of essential oils.
Because of its high nutritional value, brown rice is preferable for the large portion of the World that relies on rice as a staple food, but its longer cook time and less appealing appearance and eating quality make it a less preferred choice for the consumer. Additionally, brown rice has a shorter shelf life and this may represent a challenge for its distribution and use. Thus, a more stable product such as white rice is thought to be required. Even in areas where rice is not a staple food and a short shelf life may not be so significant, such as the United States, the superior nutritional value of brown rice makes it a better health decision. In these areas, however, white rice is still preferred due to its appearance, texture, and shorter cook times.
There have been efforts to develop a product that possess improved nutritional benefits of white rice such as increased fiber content and increased vitamin and mineral content. These efforts fall short from producing rice grains that have the desirable attributes of white rice but also contain a comparable amount of nutrients to brown rice.
For example, Squire et al. (US 2007/0054029) have developed a method to infuse fiber into a rice grain for use in rice-based cereals. In this process, soluble fiber is included in a rice cooking solution. The resultant grains are fiber-infused, but do not contain bran. Furthermore, the fiber-increasing material is limited to soluble fiber.
Satake (JP 2000-245364) has shown a rice grain coated with a bran-containing coating. The grains are mixed in a bran-containing solution and subsequently dried. Upon cooking, the bran coating may quickly separate from the grain because the bran is soluble. Consequently, coating a grain with an amount of bran higher than the disclosed amount would appear to be fruitless as the coating would simply separate from the rice grain during cooking.
In an attempt to alleviate this coating problem, Satake (JP 2003-061595) further developed a method to coat rice grains with saccharified bran. Prior to coating, bran is enzymatically saccharified to produce a viscous solution that may be coated onto the rice grain. Even with this technique, however, concentrations of only 2% (by weight) of saccharified bran are disclosed as being coated onto rice grains. Furthermore, the coating material does not include fiber and it contains only enzymatically altered bran.
To date, rice coatings have been limited to small amounts of bran because the bran easily separates from the rice grain during the cooking process. Furthermore, coating bran onto white rice to obtain a white rice-like product that is as nutritious as brown rice is counterintuitive since the bran would provide similar undesirable eating qualities as brown rice (such as chewiness) and darker color. Accordingly, a white rice grain that, when cooked, possesses similar or better nutritional value of brown rice while providing similar eating and cooking characteristics as white rice without the associated drawbacks is greatly desired.